Mark Webber says it will be "a very difficult moment" when he contemplates retiring from Formula One.

With Michael Schumacher retiring and Pedro de la Rosa without a drive after HRT closed its doors, Webber is now the oldest driver on the grid at 36 years old. The next oldest is Kimi Raikkonen - three years Webber's junior - and while Webber insists he is not thinking about retiring yet, he does admit that he is concerned about getting the timing right.

"I haven't been there yet but it is going to be a very difficult moment, no question about it," Webber told GP International magazine. "I suppose it's just about getting the timing right - not pulling the plug too early, knowing you have more to give of yourself, or going too long and not being quick enough or struggling to do the things you used to be able to do. That can become an issue as well."

2013 will be Webber's 12th season in Formula One - and seventh with Red Bull - as he continues to drive on one-year contracts.